Microstrip Patch Antennas for Broadband Indoor Wireless Systems ...

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5.0 PHASE I 5.1 RESONANT LINE METHOD: Accurately determining the dielectric constant ε r is critical to the antenna design process when designing broadband antennas. The Resonant Line method was chosen due to its ease of implementation and the return of accurate approximations. This method uses two microstrip transmission line structures as shown below: 1mm 1mm l 1 30mm 100mm 30mm 1mm l2 1mm 30mm 200mm 30mm Fig 7: Implementation of resonant line method One point to note is that, though in the illustration the lines are shown on one board, they need to be on separate boards or else coupling will occur resulting in highly inaccurate results. When a signal is fed into the input port, the gaps act as open circuits and in turn set up zero current at these points. When the signal frequency has a wavelength that is a factor (e.g. λ / 2 , λ etc) of the length of the centre section, the received signal at the output port will peak. The output will peak every time the signal wavelength matches the integral number of λ / 2 of the centre section. The wavelength ( λ ) is known and frequency of the signal can be observed using the network analyzer. The length l2 is twice the size of length l1 to compensate for the fringing effect at the ends of the patch. The equations (1) and (2) can be used to workout the dielectric constants, ε eff andε r : ε eff ⎡c = ⎣ ( ) 2 n f − n f ⎤ 1 2 2 1 ε eff ⎢ ⎥ (1) 2 f1 f 2 ( l2 − l1) ε r + 1 ε r −1 ⎛ h = + ⎜1+ 12 2 2 ⎝ W Please refer to Appendix B for a step-by-step method for ε eff andε r calculations. The results suggested an average value of 4.4 for the ε r [Refer to Appendix B]. This ε r value is lower then the G10 substrate permittivity calculated in the previous years [6]. A possible reason for this could be the use of the new milling machine. When stripping the ⎦ ⎞ ⎟ ⎠ −1/ 2 8 (2)
extra copper from the substrate, the machine removed a significant amount of substrate resulting in reduced height and ripples along the substrate plane. Due to this effect, our measurements reflected incorrect results. It was found theε r of 4.43 (2.4 GHz) using the adhesive copper tape, to be adequate where projects from previous results show an average ε r value of 4.5. 5.2 COPPER TAPE It was decided to investigate the use of adhesive copper tape to manufacture patches autonomously after a suggestion from Dr. Michael Neve; this meant the project was no longer bound by the manufacturing turn around delay period. A 3M product that fit project requirements was found and efforts were made to acquire a roll of adhesive copper tapes. Reputedly the copper tapes have been used to manufacture antennas that resonate up to 5GHz. The patches made from the copper tape, can be placed on single copper sided sheets of substrate and allow the user to create their own microstrip patch antennas without the use of any industrial machines or etching process. As a result the manufacture time can be reduced down to a few, which meant manufacture of boards was no longer PCB milling machine reliant. The copper tape allowed us to cut the copper tape to fit calculated dimensions and create desired microstrip patches. One side of the tape was adhesive; so it was possible to fix them on the substrates and in some cases overlap them. But some concerns were raised about the conductivity of the glue. An experiment was devised, to measure the transmission loss for a thin unbroken strip of copper tape. The test was repeated for a copper tape strip of identical dimensions with a missing section that was being covered by an overlapped copper tape joining the ends. The tests show (fig 8) the difference between copper strip and overlapped copper tape is minimal and can be ignored. Fig 8: Conductivity of copper tape 9
Page 1 and 2: Depart of Electrical & Electronics
Page 3 and 4: ORIGINALITY DECLARATION This report
Page 5 and 6: TABLE OF CONTENTS Page no 1.0 Intro
Page 7 and 8: 1.0 INTRODUCTION Currently there is
Page 9 and 10: 3.0 FOUNDATIONS FOR MICROSTRIP DESI
Page 11 and 12: Fig 4: Narrowband vs. Broadband Mos
Page 13: 4.0 DESIGN METHODOLOGY In order to
Page 17 and 18: Patch length of 29.66 mm was determ
Page 19 and 20: 6.0 PHASE II 6.1 BROADBANDING SCHEM
Page 21 and 22: 6.3 RECTANGULAR BROADBAND ANTENNA L
Page 23 and 24: VSWR 3 2.8 2.6 2.4 2.2 2 1.8 1.6 1.
Page 25 and 26: evident from the BLACK plot in the
Page 27 and 28: 7.0 PHASE III 7.1 AREA COVERAGE MEA
Page 29 and 30: 8.0 ISSUES TO CONSIDER FOR FUTURE R
Page 31 and 32: above in section 9.1, substrates wi
Page 33 and 34: 11.0 REFERENCE [1] Bahl, I. J and B
Page 35 and 36: APPENDIX B: - DIMENSIONS OF RECTANG
Page 37 and 38: Visual illustration showing the ind
Page 39 and 40: APPENDIX E: - BROADBAND RECTANGULAR
Page 41 and 42: APPENDIX F: - NARROWBAND TRIANGULAR
Page 43: APPENDIX H: - BROADBAND ANTENNA COM

Microstrip Patch Antennas for Broadband Indoor Wireless Systems ...

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